FMLA is granted by your employer, but the doctor is the one who says when you can return to work and if they say two weeks, your employer only legally has to hold your job for two weeks.
Like I said, I did a lot of research prior to taking leave and saw some went back as soon as 2 days after their surgery, others took the full 6 weeks, but the most common leave time was 2-6. Given that timeline and my previous experience w/ surgery, I expected 4 weeks would be the best situation for me. I am not sure there should be a "standard" for these surgeries. Most of us are very obese and have varying comorbid conditions. I'm not saying that some people cannot return at 2 weeks (or even sooner), but this should be a private conversation that takes place between a patient and their provider and should be customized to the specific patient and their needs. The door to conversation about this should not be slammed on the patient.